During the Ordovician period, a diversity of life filled the seas – cephalopods, trilobites, reef-building invertebrates and graptolites. However algae were the only multicellular plants and there was still no complex life on land.

This period is sometimes known as ‘the age of graptolites’ but it’s also importantly the era in which jawless fishes – the first vertebrates – appeared.

A mass extinction event marked the end of the Ordovician, in which more than half of all marine invertebrate species went extinct. This extinction particularly affected the trilobites, with heavy losses of shallow-water species.

Offshore along the coastline of ancient Australia there were large faults extending to the Earth’s mantle. These allowed magma (molten rock) to erupt onto the sea floor, where it cooled and hardened in the water. In this way underwater volcanoes formed and grew into chains of islands.

Today, the ocean trenches and chains of volcanic islands that we see around the western margin of the Pacific Ocean formed in exactly the same way as the ancient features.